Mobile telephony networks are well known. Mobile telephony systems, in which user equipment such as mobile handsets communicate via wireless links to a network of base stations connected to a telecommunications network, have undergone rapid development through a number of generations. The initial deployment of systems using analogue modulation has been superseded by second generation digital systems, which are themselves currently being superseded by third generation digital systems such as UMTS and CDMA. Third generation standards provide for a greater throughput of data than is provided by second generation systems; this trend is continued with the proposal by the Third Generation Partnership Project of the so-called Long Term Evolution system, often simply called LTE, which offers potentially greater capacity still, by the use of wider frequency bands, spectrally efficient modulation techniques and potentially also the exploitation of spatially diverse propagation paths to increase capacity (Multiple In Multiple Out). Typically such cellular wireless systems comprise user equipment such as mobile telephony handsets or wireless terminals, a number of base stations, each potentially communicating over what are termed access links with many user equipments located in a coverage area known as a cell, and a two way connection, known as backhaul, between each base station and a telecommunications network such as the PSTN.
A base station typically comprises a tower supporting antennas. The antennas are connected by cables to signal processors. Each signal processor includes a radio transceiver and other signal processing equipment. The signal processors are typically housed in a cabinet or other housing at ground level. The antennas are typically assigned to respective sectors around the tower and more than one antenna is typically provided per sector. For example there may be three pairs of antennas and three sectors at 120 degrees angular separation, corresponding to a cell with the result that one tower serves three sectors. The multiple antennas typically have the same radiation pattern and provide coverage for user terminals in the same area. In order to provide for independence of multiple radio propagation paths between the base station and the user terminal, the antennas may be spaced side-by-side, and/or different radiated signal polarisations may be used. One physical antenna may provide two polarisation channels. Typically, a base station sector will be provided with different polarizations, frequently + and −45 degrees, and further spatial diversity may be provided by a second dual-polar antenna. The diversity benefits arising from the use of multiple antenna channels are due to the differences in superposition or cancellation of multiple reflected signals in the radio propagation path, which cause a localised fading effect. This fading varies independently on the multiple antenna channels, due to their spatial separation or use of different radiated polarisation. When averaged over time, or over small variations in the user terminal position, the mean signal strength received from a user terminal is common. For a common azimuth angle of the user, relative to the base station sector, and for a common path loss to the user terminal, any differences in the mean received signal strength can be assumed to be due to differences in the insertion loss of the base station receiver hardware, or due to differences in the antenna gain pattern.
In some previously proposed base stations the signal processors connected to a diversity pair are associated: for example a pair of signal processors connected to a diversity pair operate at the same frequency and share a local oscillator.
In one example of a mobile telephony network, three different radio frequencies are assigned to the three sectors at a base station cell. Such a frequency re-use scheme applied to all the cells of the network ensures that no two adjacent sectors operate at the same radio frequency. Such a network is described as having a re-use of three. Single frequency networks are also known. LTE systems may be deployed either as single frequency networks, or with re-use of three.
It is important to the functioning of a base station that the configuration of the base station is correct. For example, the beam pointing directions of the antennas and the radiation patterns of the antennas should be correct. A diversity pair should point in the same direction. The beams of adjacent diversity pairs should overlap only to a predetermined extent and at predetermined positions. Furthermore a diversity pair should be connected to an associated pair of signal processors operating at the same frequency. Errors in beam pointing may occur or there may be faults in the antennas or the transceivers connected to them. Furthermore, when constructing a base station, it is not easy to correctly connect the antennas to the signal processors. The antennas are high above the housing of the signal processors and the cables for connecting them are heavy and difficult to manipulate. The height of the tower makes the manipulation of the cables potentially dangerous especially in bad weather. It is easy to incorrectly connect the cables to the antennas and signal processors. Thus there is a need to at least test a base station to determine whether there are faults in its configuration and/or to determine its configuration.